Summary There is no clinical option to restore large soft tissue defects to normal tissue structure and function. Lipoaspriates and fat transfers offer some benefits, but retention of volume and avoidance of recurring repeats of the surgeries is a major problem for large defects, such as those from surgery and trauma. Thus, sustained (retention of volume during remodeling in vivo to normal restored tissue states) soft tissue reconstruction is a major unmet clinical need, with origins in disease, surgeries and trauma. All current clinical approaches, including surgical flaps, artificial fillers, and free fat transplant ll present significant limitations. In particular, these options fail to restore native tissue size, sape and function over extended time frames; losing volume within three months of surgery. Therefore there is a critical need for new options in the field that would restore large soft tissu defects in terms of retention of volume for at least one year during tissue integration and regeneration in vivo. To address this need, we propose to implement a 3D porous silk-based protein biomaterial scaffold system in combination with lipoaspirate. The unique features of the system include the ability to stabilize the silk protein matrix used in vivo for more than a year yt achieve full native tissue regeneration over time, the ability to support cells and promote adipogenesis and vasculogenesis, the mechanical robustness of the scaffold system to support tissue structure and volume over time, and the use of a biocompatible, FDA approved, biomaterial (silk) in the process. The hypothesis is that a biomaterial system can be designed for soft tissue reconstruction needs where size and shape at the implant site can be retained for at least one year during vascularized adipose formation, and allow full integration with native tissue with complete remodeling over time. Our comprehensive preliminary data support the feasibility of the plan and the aim is designed to demonstrate the best path forward in a three month in vivo mouse study. We will assess variables of cell adhesion sites (RGD), and the role of lipoaspirate in the process. Unseeded control scaffolds will also be studied. Outcomes will include assessments against other commonly considered biodegradable polymeric materials (collagen, PLGA, PCL): (a) retention of size and shape for 3 months in vivo, and (b) vascularized adipose tissue distribution in the scaffold, and (c) integration with surrounding tissue. At the end of the study we anticipate being in a position to pursue long term large animal studies and then human clinical trials. PUBLIC HEALTH RELEVANCE: The need for stable soft tissue reconstruction is large and growing due to severe trauma, diseases such as cancer and surgery. However, current clinical options are limited. The proposed program will address this need and fill the current gap in available clinical options in terms of retention of volume and shape of the defect site during tissue regeneration.